Feeders for feeding workpieces in the metal processing industries have recently been proposed in which a reduction of noise is the object. In these arrangements a bar stock is fed through the interior of tubes. However, in practice it transpires that as soon as the bars begin to revolve inside their tubes they still generate a considerable amount of unwelcome noise. The volume of this noise depends upon the cross section of the bar stock that is to be machined. In other words, if the bar stock has a polygonal cross section, e.g. a hexagonal, octagonal or dodecagonal cross section, the generated noise, compared with that generated by bars of circular cross section becomes progressively greater.
For the purpose of muffling the loud noise that arises when the bar stock is rotated, an expedient that has been tried is to provide the inside surface of the conveying tubes with a lining of rubber or of some such material that has a sound absorbing effect.
Work feed tubes are also known which contain a coil spring that can be withdrawn in the radial direction and that is intended to prevent the bar material from clanging against the inside of the tube.
Moreover, for more silently feeding a bar stock tubes have been used which contain displaceable sleeves resembling bushes.
However, all the above describing devices for reducing the noise of feeding bar stock suffer from the common drawback that the bars which may often not be exactly horizontal are responsible for a high rate of wear of the sound suppressing materials and the associated machine elements. This is so more particularly in the case of feeder tubes for bar stock containing an internal lining.
Moreover, owing to the direct or indirect contact that takes place between the feeding bar stock and the feeder tube it is impossible to prevent the build-up of vibrations which contrary to the desired sound suppressing effect tend to amplify and intensify the noise. Furthermore, known types of feeders for bar stock do not ensure that the bars move centrally through the feeder. This has an adverse effect upon the production of precision components from the stock.
Another drawback is that if trouble should arise in the feeder, the preferably divided tube must be opened. This causes loss of time and therefore increases costs.
A noise reducing bar stock feeder has also been proposed which differs from other devices in that a plurality of mounts each provided with an axial bore are located at equidistant intervals on a beam, each mount containing three bearing balls which make contact with the bar. Each ball is rotatably mounted on an eccentric pin. A feeder tube provided with an internal lining is not used in this arrangement.
It is a defect of this latter arrangement that the diameter of the openings for the passage therethrough of the bars determines the diameters or overall dimensions of the bars the feeder can handle. Another defect is that bar stock having a profiled cross section is altogether unsuitable for such a feeder.